A communication system may provide communication services that include wireless radio transmission of digitized speech, still or moving images, text messages, position location determination and other types of data. Such communication services may be provided to a type of devices that are mobile, such as a cellular phone, a portable computer, etc. A communication system through a collection of commonly known cell sites provide the communication services without interruption over a broad range of areas to a mobile station. Each cell site may include a base transceiver station and control units. One cell site may have more than one base transceiver stations. Each base transceiver station provides the radio frequency link over a limited geographical area. When a mobile station moves from a location to another, the mobile station may go through a handed off process that allows providing the communication services without interruption. The handoff may be accomplished through a soft hand off or a hard handoff or both. In soft handoff, the mobile station receives essentially identical traffic channel data from at least two base transceiver stations over a common carrier frequency. The base transceiver stations involved in the soft handoff process may be located in two different cell sites or the same cell site. In hard handoff, the resources in a current base station transceiver are released while new communication resources in a new base station are allocated to the user. In hard handoff, the carrier frequency of the current base station may be different than the carrier frequency of the new base station. As such, generally, hard handoff occurs between cell sites that are operating over two different frequencies. Inter-frequency hard handoff can also take place between two frequency assignments in the same cell or same sector.
The process for the hard handoff may be preceded by a search for possible hard handoff candidates including pilot signals belonging to the candidate frequencies. The search may be performed by the mobile station at any time including the time when the mobile station is moving from one cell site to another. The mobile station may need to search for possible hard handoff candidates while maintaining a traffic call with a base station. The receiver portion of the mobile station may need to be tuned to different frequencies for finding a new hard handoff candidate. The mobile station may have only one receiver portion. Therefore, during the search time, the traffic of data on the traffic channel between the current base station and the mobile station may be disrupted or the mobile station may mute the incoming voice information. As such, there may be a substantial delay in delivery of data or suspension of voice traffic data during the search period. Similarly, a single receiver is not capable to maintain two-way communications and global positioning system (GPS) reception for position location determination. The GPS system operates on an independent frequency band.
To this end as well as others, there is a need for a receiver and a method for providing un-interrupted communication services in a communication system.
A method and apparatus in a communication system provide for concurrent processings of signals at the different frequencies. A received signal is down converted in a RF/IF system to produce on-channel and out-of-channel received samples. The on-channel received samples are processed in a back-end portion to decode on-channel information. The out-of-channel received samples are processed to determine at least one of a link quality and global positioning system originated information in the back-end portion. The processings of the on-channel received samples and the out-of-channel received samples are performed essentially at the same time by the receiver back-end.